1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device having a thin film transistor substrate with a multi-cell gap structure, and a method of manufacturing same.
2. Description of the Related Art
The liquid crystal display is a common type of display seen in a variety of portable electronic products, such as notebook computers and in some desktop computer monitors. Liquid crystal displays are lightweight, consume low power and are capable of outputting images having high resolution.
Liquid crystal displays generally consist of a pair of panels or substrates that include electrodes and polarizers, and a liquid crystal layer interposed between the panels. The liquid crystal layer is disposed between electrodes on opposing panels, which apply a voltage across the liquid crystal layer. Variations in the applied voltage alter the molecular orientation of the liquid crystal layer, resulting in different images that are displayed. The gap between the electrodes that is filled by the liquid crystal layer is known as the cell gap.
Liquid crystal display devices have been classified into transmission type and reflection type, the classification depending on whether the light source is internal or external to the liquid crystal display device. The transmission type liquid crystal display device displays an image using light generated from inside the liquid crystal display device. Conversely, the reflection type liquid crystal display device displays an image using light generated from outside the liquid crystal display device.
A third type of liquid crystal display device, which uses light from both internal and external sources is also known. This liquid crystal device is appropriately referred to as a reflection-transmission type liquid crystal display device.
FIG. 1 is a sectional view showing a conventional reflection-transmission type liquid crystal display device 50. Referring to FIG. 1, the reflection-transmission type liquid crystal display device 50 includes a thin film transistor substrate 10, a color filter substrate 20 and a liquid crystal layer 30 interposed between the thin film transistor substrate 10 and the color filter substrate 20.
The thin film transistor substrate 10 includes a first substrate 11, a thin film transistor 12, an insulating layer 13 and a pixel electrode 16. The thin film transistor 12 includes a gate electrode 12a, a gate insulating layer 12b, a semiconductor layer 12c, a source electrode 12d and a drain electrode 12e. The insulating layer 13 is formed on the first substrate 11 and covers the thin film transistor 12. The insulating layer 13 is provided with a contact hole 13a for exposing the drain electrode 12e. 
The pixel electrode 16 is formed on the insulating layer 13 and is electrically connected to the drain electrode 12e through the contact hole 13a. The pixel electrode 16 includes a transmission electrode 14 and a reflection electrode 15. The reflection electrode 15 is formed on the transmission electrode 14 and defines a reflection region R for reflecting external light R1. In order to define a transmission region T for transmitting internal light R2, a predetermined section of the reflection electrode 15 is removed to expose the transmission electrode 14.
The color filter substrate 20 includes a second substrate 21, a color filter layer 22 formed on the second substrate 20 and consisting of red, green and blue (R, G and B) color pixels. A common electrode 23 is formed on the color filter layer 22 and corresponds to the pixel electrode 16 of the thin film transistor substrate 10.
A first retardation plate 41 (i.e., an optical element that produces, for example, full, half or quarter wave phase changes of polarized light) and a first polarizing plate 45 are provided at a lower portion of the thin film transistor substrate 10, and a second retardation plate 42 and a second polarizing plate 46 are positioned at an upper portion of the color filter substrate 20.
The conventional reflection-transmission type liquid crystal display device 50 reflects external light R1 through the reflection region R and transmits internal light R2 through the transmission region T, thereby displaying an image.
However, the conventional reflection-transmission type liquid crystal display device 50 has a disadvantage in that its design is based on a reflection type liquid crystal device and the characteristics of light passing through the reflection region R. Known reflection-transmission type liquid crystal display devices do not take into account the different characteristics of light passing through a transmission region T and the need for a different structure to optimize usage of this light. In known reflection-transmission type devices, the transmittance of the transmission region T is reduced by half as compared with that of the transmission type liquid crystal display devices. Optical conditions of the known reflection-transmission type liquid crystal display devices, which are designed on the basis of only the reflection region R, make it impossible to use 100% of the polarized light in the transmission region T.
Therefore, there exists a need for a design of a reflection-transmission type liquid crystal display device that takes into account the characteristics of light passing through both reflection and transmission regions and maximizes usage of light in the transmission region.